In recent times, nano-sized metal chalcogenides materials have been the subject of significant research due to their potential applications as biological markers, nonlinear optical materials, luminescent devices, photodetectors, catalysts, chemical sensors and in highly effective UV-protective coatings, etc. One known method to prepare metal chalcogenide nanomaterials involves reaction in a confined medium such as microemulsion or polymer matrix whereby difficulty has been encountered in producing particles of uniform sizes.
Although a large variety of synthesis approaches have been reported for the preparation of crystalline metal chalcogenides, the large-scale synthesis or mass production of nano-sized metal chalcogenides is still a challenge. Metal chalcogenides can be prepared using a variety of wet-chemical methods including sol-gel, co-precipitation, and hydrothermal synthesis.
The extensively applied sol-gel or co-precipitation procedures are based on the hydrolysis and condensation of metal halides or metal alkoxides as precursors in aqueous solution. However, these methods suffer some major drawbacks. For example, the as-synthesized particles are amorphous and subsequent heat treatment is necessary to induce crystallization. However, this additional step results in alteration, mainly particle growth, or even in destruction of the particle morphology. Further disadvantages of aqueous systems are reaction parameters that are difficult to control, such as fast hydrolysis rate of the metal alkoxides, pH, method of mixing, rate of oxidation or sulfuration and especially the nature and concentration of anions. Also, high temperatures (higher than 500° C.) are required to calcine or hydrothermally treat the intermediate to obtain crystalline metal chalcogenides. This has a negative effect on the finely divided nature since the particles are subjected during this treatment to form μm-sized aggregates which can be broken down only incompletely to the primary particles by grinding.
Another problem that plagues some of the known processes is the poor physical stability of the nanoparticles in dispersion medium that are formed. In these processes, the chemical reactions that lead to the precipitation of the metal chalcogenides particle inevitably result in the formation of by-products. Insufficient removal of the by-products adversely affects the monodispersibility of the nanoparticles in medium, which results in agglomerations of impure metal chalcogenide particles being formed. Furthermore, even when pure metal chalcogenide particles have been formed, the by-products can be difficult to remove. In light of the aforementioned problem of poor dispersibility of metal chalcogenide particles, improvisations of current synthesis methods have been carried out to enhance the physical stability of the metal chalcogenide particles. However, the solid loading percentages of substantially stable metal chalcogenide particles suspensions obtained by these methods are far from ideal, typically at a solid loading percentage of less than 5%. The low solid loading percentage of the suspensions translates to storage inefficiency for the particles suspensions.
There is a need to provide a process of making metal chalcogenide particles that overcomes, or at least ameliorate, one or more of the disadvantages described above.
There is a need to provide a process of making metal chalcogenide particles that is able to separate any by-products from metal chalcogenide particles that are substantially free of by-products.
There is a need to provide highly concentrated substantially monodispersed metal chalcogenides nanoparticle dispersion that overcomes, or at least ameliorates, one or more of the disadvantages described above.